Acceleration sensitive damping for automotive dampers

ABSTRACT

A shock absorber having a pair of valve assemblies which include an acceleration sensitive valve which couples the working chamber of the shock absorber to the shock absorber&#39;s reservoir chamber through a fluid path to provide a soft damping characteristic for the shock when the shock absorber experiences acceleration beyond a specific amount. A compression valve assembly and a rebound valve assembly are also provided which controls the fluid flow through the piston and the base assembly, respectively, to provide a firm damping characteristic for the shock absorber during low acceleration movement.

FIELD OF THE INVENTION

The present invention relates generally to automotive dampers or shockabsorbers which receive mechanical shock. More particularly, the presentinvention relates to automotive dampers or shock absorbers which aresensitive to accelerations imposed upon the damper or shock absorber toswitch between a firm and a soft damping characteristic.

BACKGROUND OF THE INVENTION

Shock absorbers are used in conjunction with automotive suspensionsystems to absorb unwanted vibrations which occur during driving. Toabsorb unwanted vibrations, shock absorbers are generally connectedbetween the sprung portion (body) and the unsprung portion (suspension)of the automobile. A piston is located within a pressure tube of theshock absorber and is connected to the sprung portion of the automobilethrough a piston rod. The piston divides the pressure tube into an upperworking chamber and a lower working chamber. Because the piston is able,through valving, to limit the flow of damping fluid between the upperand lower working chambers when the shock absorber is compressed orextended, the shock absorber is able to produce a damping force whichcounteracts the vibration which would otherwise be transmitted from theunsprung portion to the sprung portion of the automobile. In a dual tubeshock absorber, a fluid reservoir is defined between the pressure tubeand the reservoir tube. A base valve is located between the lowerworking chamber and the reservoir to limit the flow of fluid between thelower working chamber and the reservoir to produce a damping force whichalso counteracts the vibration which would otherwise be transmitted fromthe unsprung portion to the sprung portion of the automobile. Thegreater the degree to which the flow of fluid within the shock absorberis restricted by the piston valving or the base valve, the greater thedamping forces which are generated by the shock absorber. Thus, a highlyrestricted flow of fluid would produce a firm ride while a lessrestricted flow of fluid would produce a soft ride.

In selecting the amount of damping that a shock absorber is to provide,at least three vehicle performance characteristics are considered. Thesethree characteristics are ride comfort, vehicle handling and roadholding ability. Ride comfort is often a function of the spring constantof the main springs of the vehicle as well as the spring constant of theseat, tires and the damping coefficient of the shock absorber. Foroptimum ride comfort, a relatively low damping force or a soft ride ispreferred. Vehicle handling is related to the variation in the vehicle'sattitude (i.e. roll, pitch and yaw). For optimum vehicle handling,relatively large damping forces or a firm ride are required to avoidexcessively rapid variations in the vehicle's attitude during cornering,acceleration and deceleration. Road holding ability is generally afunction of the amount of contact between the tires and the ground. Tooptimize road handling ability, large damping forces are required whendriving on irregular surfaces to prevent loss of contact between thewheel and the ground for excessive periods of time.

Various methods for selectively changing the damping characteristics ofa shock absorber in response to the operational characteristics of thevehicle have been developed. Continued development of shock absorbershave been directed towards simplified and low cost systems whicheffectively control the damping characteristics of the shock absorber inresponse to the varied operational characteristics of the vehicle.

SUMMARY OF THE INVENTION

The present invention provides the art with a dual or twin tube shockabsorber which incorporate an acceleration sensitive valving systembetween the working tube and the reserve tube. The dual tube shockabsorber is sensitive to accelerations imposed on the shock absorberduring movement of the acceleration valve assembly.

Other advantages and objects of the present invention will becomeapparent to those skilled in the art of subsequent detailed description,appended claims and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings in which the best mode presently contemplated forcarrying out the invention:

FIG. 1 is an illustration of an automobile using the automaticallyadjustable damping system in accordance with the present invention;

FIG. 2 is a cross-sectional view of the automatic damping system withthe acceleration valve incorporated into the upper end cap;

FIGS. 3a and 3 b depict the acceleration valve as shown in FIG. 2 in itsopen and closed positions; and

FIG. 4 is a side view, partially in cross-section, of a shock absorberincorporating the automatically adjustable damping system in the basevalve in accordance with another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

Referring now to the drawings in which like reference numerals designatelike or corresponding parts throughout the several views, there is shownin FIG. 1 a vehicle incorporating a suspension system having theautomatically adjustable shock absorbers in accordance with the presentinvention which is designated generally by the reference numeral 10.Vehicle 10 includes a rear suspension 12, a front suspension 14 and abody 16. Rear suspension 12 has a transversely extending rear axleassembly (not shown) adapted to operatively support the vehicle's rearwheels 18. The rear axle assembly is operatively connected to body 16 bymeans of a pair of shock absorbers 20 and a pair of helical coil springs22. Similarly, front suspension 14 includes a transversely extendingfront axle assembly (not shown) to operatively support the vehicle'sfront wheels 24. The front axle assembly is operatively connected tobody 16 by means of a second pair of shock absorbers 26 and by a pair ofhelical coil springs 28. Shock absorbers 20 and 26 serve to dampen therelative motion of the unsprung portion (i.e. front and rear suspensions12 and 14, respectively) and the sprung portion (i.e. body 16) ofvehicle 10. While vehicle 10 has been depicted as a passenger car havingfront and rear axle assemblies, shock absorbers 20 and 26 may be usedwith other types of vehicles or in other types of applications such asvehicles incorporating independent front and/or independent rearsuspension systems. Further, the term “shock absorber” as used herein ismeant to refer to dampers in general and thus will include MacPhersonstruts.

Referring now to FIG. 2, shock absorber 20 is shown in greater detail.While FIG. 2 shows only shock absorber 20, it is to be understood thatshock absorber 26 also includes the piston, the base valving and theacceleration sensitive valving described below for shock absorber 20.Shock absorber 26 only differs from shock absorber 20 in the way inwhich it is adapted to be connected to the sprung and unsprung portionsof vehicle 10. Shock absorber 20 comprises a pressure tube 30, a piston32, a piston rod 34, a reservoir tube 36 and a base valve assembly 40.

Pressure tube 30 defines a working chamber 42. Piston 32 is slidablydisposed within pressure tube 30 and divides working chamber 42 into anupper working chamber 44 and a lower working chamber 46. A seal 48 isdisposed between piston 32 and pressure tube 30 to permit slidingmovement of piston 32 with respect to pressure tube 30 withoutgenerating undue frictional forces as well as sealing upper workingchamber 44 from lower working chamber 46. Piston rod 34 is attached topiston 32 and extends through upper working chamber 44 and through anupper end cap 50 which closes the upper end of both pressure tube 30 andreservoir tube 36. A sealing system 52 seals the interface between upperend cap 50, reservoir tube 36 and piston rod 34. The end of piston rod34 opposite to piston 32 is adapted to be secured to the sprung portionof vehicle 10. Valving within piston 32 controls the movement of fluidbetween upper working chamber 44 and lower working chamber 46 duringmovement of piston 32 within pressure tube 30. Because piston rod 34extends only through upper working chamber 44 and not lower workingchamber 46, movement of piston 32 with respect to pressure tube 30causes a difference in the amount of fluid displaced in upper workingchamber 44 than the amount of fluid displaced in lower working chamber46. This difference in the amount of fluid displaced is known as the“rod volume” and it flows through base valve assembly 40.

Reservoir tube 36 surrounds pressure tube 30 to define a reservoirchamber 54 located between the tubes. The bottom end of reservoir tube36 is closed by a lower end cap 58 which is adapted to be connected tothe unsprung portions of vehicle 10. The upper end of reservoir tube 36is attached to upper end cap 50. Base valve assembly 40 is disposedbetween lower working chamber 46 and reservoir chamber 54 to control theflow of fluid between the two chambers. When shock absorber 20 extendsin length, an additional volume of fluid is needed in lower workingchamber 46 due to the “rod volume” concept. Thus, fluid will flow fromreservoir chamber 54 to lower working chamber 46 through base valveassembly 40. When shock absorber 20 compresses in length, an excess offluid must be removed from lower working chamber 46 due to the “rodvolume” concept. Thus fluid will flow from lower working chamber 46 toreservoir chamber 54 through base valve assembly 40.

Referring now to FIGS. 2, 3 a and 3 b, an acceleration sensitive valveassembly 60 is incorporated into upper end cap 50. Accelerationsensitive valve assembly 60 comprises an outer housing 62, a valve body64, a seal 66, a spring or biasing member 68 and a retainer 70. Upperend cap 50 is secured to the end of the pressure tube 30 and the end ofreservoir tube 36 by being pressed into pressure tube 30 and reservoirtube 36 or by other means well known in the art. Outer housing 62 ispress fit or otherwise secured within a bore 72 defined by upper end cap50. A fluid passage 74 connects bore 72 with upper working chamber 44.Outer housing 62 defines a central cavity 76 which is in fluidcommunication with reservoir chamber 54, bore 72 and passage 74. Valvebody 64 is disposed within cavity 76 and seal 66 is disposed betweenouter housing 62 and valve body 64 to seal cavity 76 from reservoirchamber 54. Spring 68 is disposed between retainer 70 and valve body 64to bias valve body 64 against seal 66 to maintain the seal betweencavity 76 and reservoir chamber 54.

During a compression stroke for shock absorber 20, fluid within lowerworking chamber 46 is pressurized. A check valve assembly 80 associatedwith piston 32 allows fluid flow from lower working chamber 46 to upperworking chamber 44. Due to the “rod volume” concept described above,during the compression stroke fluid flow must also occur from workingchamber 44 to reservoir chamber 54 through base valve assembly 40. Basevalve assembly 40 includes a compression valve assembly 82 which opensunder the influence of fluid pressure within lower working chamber 46 toallow the fluid to flow from lower working chamber 46 to reservoirchamber 54. The damping forces generated by shock absorber 20 during acompression stroke are controlled by the design of compression valveassembly 82.

During a rebound stroke of shock absorber 20, fluid within upper workingchamber 44 is pressurized. A rebound valve assembly 84 associated withpiston 32 opens under influence of fluid pressure within upper workingchamber 44 to allow the flow of fluid from upper working chamber 44 tolower working chamber 46. The damping forces generated by shock absorber20 during a rebound stroke are controlled by the design of rebound valveassembly 84. Due to the “rod volume” concept described above, during therebound stroke fluid flow must also occur from reservoir chamber 54 tolower working chamber 46. Base valve assembly 40 includes a check valveassembly 86 which allows fluid flow from reservoir chamber 54 to lowerworking chamber 46.

Acceleration sensitive valve assembly 60 functions during a reboundstroke to allow fluid flow from upper working chamber 44 to reservoirchamber 54 when shock absorber 20 experiences a prespecified amount ofacceleration. This additional or secondary fluid flow reduces thestiffness of shock absorber 20 during the rebound stroke. As wheels 18or 24 receive an input, reservoir tube 36, pressure tube 30 and upperend cap 50 are accelerated. This acceleration works on the mass of valvebody 64 perpendicular to the longitudinal axis of valve body 64,resulting in a moment about seal 66 due to the overhanging mass featureof valve body 64. Spring 68 also creates a moment about seal 66. At thepoint where the acceleration induced moment exceeds the spring forceinduced moment, valve body 64 becomes unstable and rotates about theedge of seal 66 resulting in a hydraulic leak path 88 as shown in FIG.3b. When leak path 88 is open, hydraulic fluid flows from upper workingchamber 44, through passage 74 and through cavity 76 into reservoirchamber 54. This flow reduces the hydraulic fluid pressure within upperworking chamber 44 resulting in lower damping forces and a softer ride.

The configuration of valve body 64 is such that hydraulic pressurewithin upper working chamber 44 will work to stabilize valve body 64. Asdamper velocity increases and therefore hydraulic pressure, greater andgreater wheel accelerations will be necessary to destabilize valve body64. This characteristic will tend to “filter” the wheel inputs thatdestabilize valve body 64, effectively reducing a valve sensitivity tothose inputs inducing a high frequency, low amplitude signal at theconnection of shock absorber 20 to the unsprung mass of the vehicle.

Referring now to FIG. 4, an alternative embodiment of the presentinvention is illustrated. In FIG. 4, acceleration sensitive valveassembly 60 is illustrated as being incorporated into base valveassembly 40 between lower working chamber 46 and reservoir chamber 54.In this position, acceleration sensitive valve assembly 60 reacts toacceleration forces during a compression stroke to reduce the dampingforces and provide a soft ride in the same manner as that describedabove when valve assembly 60 is located within upper end cap 50.

While not specifically illustrated, it is within the scope of thepresent invention to provide acceleration sensitive valve assembly 60 inboth upper end cap 50 and base valve assembly 40 to provide variabledamping in both rebound and compression if desired.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention.

What is claimed is:
 1. A damper comprising: a pressure tube forming aworking chamber and defining a damper axis; a reservoir tube disposedaround said pressure tube, said reservoir tube forming a reservoirchamber between said pressure tube and said reservoir tube; a base valveassembly disposed between said working chamber and said reservoirchamber for regulating flow of damping fluid between said workingchamber and said reservoir chamber, said base valve assembly comprising:an end cap attached to said pressure tube; a first pressure responsivevalve attached to said end cap, said pressure responsive valvecomprising a valve body attached to said end cap, and a valve diskdisposed between said valve body and said end cap; and an accelerationresponsive valve disposed between the reservoir tube and the pressuretube, said acceleration valve comprising an outer housing defining acavity in communication with said reservoir chamber and said workingchamber, and a valve body disposed within said cavity, said valve bodydefining a valve axis, said valve body being movable between a firstposition where said valve axis is not perpendicular to said damper axisand said reservoir chamber is in communication with said working chamberand a second position where said valve axis is perpendicular to saiddamper axis and said reservoir chamber is not in communication with saidworking chamber.
 2. The damper according to claim 1 further comprising apiston disposed within said working chamber, said piston dividing saidworking chamber into an upper portion and a lower portion, saidacceleration responsive valve being disposed between said lower portionof said working chamber and said reservoir chamber.
 3. The damperaccording to claim 1 wherein said valve body is biased towards saidsecond position.
 4. The damper according to claim 1 wherein said basevalve assembly further comprising a biasing member for urging saidacceleration responsive valve into said second position.
 5. A dampercomprising: a pressure tube forming a working chamber being filled withdamping fluid; a reservoir tube disposed around said pressure tube, saidreservoir tube forming a reservoir chamber between said pressure tubeand said reservoir tube; a base valve assembly disposed between saidworking chamber and said reservoir chamber for regulating flow of saiddamping fluid between said working chamber and said reservoir chamberthrough a first flow path; an acceleration responsive valve disposedbetween said working chamber and said reservoir chamber for regulatingflow of said damping fluid between said working chamber and saidreservoir chamber through a second flow path, said second flow pathbeing totally separate from said first flow path, said accelerationresponsive valve comprising an outer housing defining a cavity incommunication with said reservoir chamber and said working chamber, anda valve body disposed within said cavity, said valve body defining avalve axis, said valve body being movable between a first position wheresaid valve axis is not perpendicular to said damper axis and saidreservoir chamber is in communication with said working chamber and asecond position where said valve axis is perpendicular to said damperaxis and said reservoir chamber is not in communication with saidworking chamber.
 6. The damper according to claim 5 further comprising apiston dividing said working chamber into an upper working chamber and alower working chamber, said acceleration responsive valve being disposedbetween said upper working chamber and said reservoir chamber.
 7. Thedamper according to claim 5 further comprising a piston dividing saidworking chamber into an upper working chamber and a lower workingchamber, said acceleration responsive valve being disposed between saidlower working chamber and said reservoir chamber.
 8. The damperaccording to claim 5 wherein said valve body is biased towards saidsecond position.